Math is Scary - Drowning is (probably) Scarier

[АлександрД]

Just want to remind
In reality - metric system is much more suitable for fast estimations in diving.
Also exists Ratio decompression - Wikipedia - "a little bit advanced calculations in mind"

So, in my experience, latest times I use just two SPG values:
- "Enough!", or "More than enough!"
and
- "OPS " (or "Upsss...", depends on prononsiations in regions). I say Опаньки (Opan`kee)

and meaning of this two values is very simple.
- Enough - you can relax and just have a dive.
- Ops - you should start to go back to the surface.

Just one adjusting point - pressure, where you deside to be "Ops"

and this point depends on diving conditions.
- for shallow dive - you can keep it without any problems at 50bar (725 psi) or even below.
- for deep dives in the blue - you should keep it at half of the pressure
- for deep dive with slow ascending along the bottom profile - you can keep it at 50 bar - 70 bar (725 - 1015 psi)
- for cave dives - you never should dive to the caves with recreational experience and this methodics

It is just my opinion for easy diving conditions. Never offer this to follow. Just as another way to calculate air reminder.

 

[Manatee Diver]

In reality - metric system is much more suitable for fast estimations in diving.

Not really, if you are doing fast estimations tank factors are good enough.

AL80 2.5 cuft per 100 psi
HP100 2.9 cuft per 100 psi
LP85 3.2 cuft per 100 psi

The rest are easy to calculate, I know those off the top of my head as those are the tanks I own.

 

[rddvet]

Not really, if you are doing fast estimations tank factors are good enough.

AL80 2.5 cuft per 100 psi
HP100 2.9 cuft per 100 psi
LP85 3.2 cuft per 100 psi

The rest are easy to calculate, I know those off the top of my head as those are the tanks I own.

I pretty much only use our lovely american standard, but he was right. When you start doing gas calculations for things like scooter or bailout ranges, Metric really is easier. I've been saying I'm going to move to BAR for years, but haven't yet just because I'm more familiar with our imperial system. And I haven't had to buy new spgs in a while and don't want to buy new ones just to have metric readings

 

[Manatee Diver]

I pretty much only use our lovely american standard, but he was right. When you start doing gas calculations for things like scooter or bailout ranges, Metric really is easier. I've been saying I'm going to move to BAR for years, but haven't yet just because I'm more familiar with our imperial system. And I haven't had to buy new spgs in a while and don't want to buy new ones just to have metric readings

I can do them in both and just don't find them any easier, just divide by 10 vs 33, and divide by tank factor instead of water capacity.

Now some of the calculations like with gas laws and heating and such, I switch to metric because yeah it is easier. But I think that is because I learned them all in metric due to chemistry. In fact I did the entire SSI Science of Diving course (when it was free during COVID) in metric because I thought it would contain actual science.

Of course I can point at one of the advantages of AI, it is just a couple of menu options to switch to metric. Of course all my SPGs for back ups, and stages are in PSI.

 

[Storker]

I can do them in both and just don't find them any easier, just divide by 10 vs 33, and divide by tank factor instead of water capacity.

Do you seriously think that dividing by 33 is just as easy as dividing by 10?

Perhaps we on the right side of the pond are stupider than y'all on the left side of the pond, but even with a STEM college degree, I find it a lot easier to divide by 10. Just move the decimal point.

And at 30+ meters, I'm going to keep stuff as dumbed down as I can. Because I get stupid at those depths. Like, below median Idiocracy stupid.

 

[dmaziuk]

Do you seriously think that dividing by 33 is just as easy as dividing by 10?

We need to switch to base-12. Then dividing by 2, 3, or 4 will be easy while dividing by that Yurrupean 10: too hard.

 

[Storker]

We need to switch to base-12. Then dividing by 2, 3, or 4 will be easy while dividing by that Yurrupean 10: too hard.

Good luck lobbying that change

 

[Manatee Diver]

Do you seriously think that dividing by 33 is just as easy as dividing by 10?

Perhaps we on the right side of the pond are stupider than y'all on the left side of the pond, but even with a STEM college degree, I find it a lot easier to divide by 10. Just move the decimal point.

And at 30+ meters, I'm going to keep stuff as dumbed down as I can. Because I get stupid at those depths. Like, below median Idiocracy stupid.

Because I don't do that type of math underwater, that is all pre-dive planning that is done with a cellphone so 10 vs 33/34 is a minor change. By the time I hit the water we just have minor changes in the plan based on the real amount of gas in my tanks after cooling. And underwater I dive the plan, any math is real rough math with a healthy dose of conservatism.

 

[BlueTrin]

We need to switch to base-12. Then dividing by 2, 3, or 4 will be easy while dividing by that Yurrupean 10: too hard.

A perfectly logical decision

 

[EFX]

Because I don't do that type of math underwater, that is all pre-dive planning that is done with a cellphone so 10 vs 33/34 is a minor change. By the time I hit the water we just have minor changes in the plan based on the real amount of gas in my tanks after cooling. And underwater I dive the plan, any math is real rough math with a healthy dose of conservatism.

My sentiments exactly. I suppose it's a good check on the reliability of the SPG. At some point they're going to wear out and give erroneous readings, at least the mechanical gauges. But, honestly, I'm just too lazy to do the math, even simpler approximations. I'm not sufficiently bored with my diving or scared enough to take on any calculations underwater.

I had to go back to the first post to see who this advice was meant for. It was directed to new divers. I read through the article on SAC and gas usage calculations and found the advice sound enough, but came away thinking this is putting "the cart before the horse". We need to get those new divers to pay more attention to their SPG'S especially on deeper dives. The overriding assumption of the article is that the SAC rate doesn't vary. At least, not enough to make gas usage calculations useless. But, that is the problem with new and "newish" divers; Their SAC rates are changing due to inexperience to changing environmental and dive conditions. Once divers get comfortable and their SAC rates stabilize then I can see some merit in these calculations.

Edit: if you are worried about your SPG reading correctly, get it tested regularly or replace it.